Dental implant systems are known, which include a dental implant, or a portion that is adapted to be inserted and bound to the jawbone; an abutment that is adapted to be inserted into the implant; a locking screw that is adapted to be screwed inside the implant and to lock the abutment to the implant; and a prosthesis that simulates a missing tooth and that is adapted to be bound to the abutment.
U.S. patent publication no. 2009/0239196 discloses a dental implant system comprising a dental implant, an abutment and a locking screw. The implant generally has a substantially cylindrical and elongated body, which is provided with an externally threaded portion for screwing into the jawbone of a patient, and with a blind inner hole configured for receiving the abutment and the locking screw.
The blind inner hole has, in descending order, a frustoconical first portion with an upperly widening portion, a cylindrical second portion, and a threaded third portion receiving the locking screw.
The abutment instead includes a substantially cylindrical elongated body, with an insertion portion adapted for inserting into the blind hole of the implant and with an outer surface conformed to mate with the surface of the blind inner hole of the implant. In particular, the insertion portion includes, in descending order, an upperly widening frustoconical first portion that mates with the frustoconical first portion of the blind inner hole of the implant, and a cylindrical second portion.
The abutment also has an axial through-hole for receiving the locking screw.
The locking screw includes an elongated cylindrical body configured for inserting in the through-hole of the abutment, and a threaded portion configured for screwing in the threaded third portion of the inner blind hole of the implant, causing the abutment to become coupled to the implant.
The axial hole of the abutment includes a frustoconical portion widening in an upper direction, which corresponds to a frustoconical portion of the head of the locking screw, where the inclination of the frustoconical portion is less than 15° from the longitudinal axis.
International publication no. WO 2006/128620 discloses a dental implant system that includes an abutment provided with guiding and locking means for joining the abutment to the dental implant.
In particular, the abutment includes a portion adapted for inserting into the blind hole of the implant and further includes, in descending order, a substantially frustoconical first portion that has a wider upper end, a second portion having anti-rotational means, and a third portion that operates as a guide for inserting the abutment into the blind hole.
Further, the abutment has an axial opening for inserting the locking screw that couples the abutment to the implant.
Dental implant systems must bear significant loads, especially during mastication.
In the known systems, the frustoconical contact surface between the inside of the abutment and the locking screw is substantially level with, and for the most part above, the crest line in case of standard positioning.
More generally, in the event of an above crest or below crest positioning, the frustoconical surface becomes mostly positioned above the connecting circumference, corresponding to the real junction circumference among the different frustoconical surfaces.
For ease of discussion, reference will be made hereinafter to the crest/connection line, so as to include all possible situations.
In fact, the elevational midpoints of the contact frustoconical surface between the inside of the abutment and the locking screw defines a circumference, hereinafter called a median circumference. That medial circumference is substantially above the crest/connection line.
Consequently, all loads are unbalanced upwardly and frequently cause ruptures of parts of the implant system, for example, of the collar of the implant, where the majority of mastication loads are concentrated.